Bistable frequency fuze system for vt fuze

ABSTRACT

1. In a bistable frequency fuze system for variable time fuzes, the combination comprising: A. A RADIO FREQUENCY OSCILLATOR DETECTOR FOR PRODUCING OUTPUT SIGNALS IN RESPONSE TO RECEIVED SIGNALS APPEARING AS SIGNALS REFLECTED FROM A TARGET, B. A BISTABLE TRIGGER CIRCUIT BEING COUPLED TO SAID OSCILLATOR DETECTOR FOR PRODUCING FIRST AND SECOND OUTPUT VOLTAGES IN RESPONSE TO OUTPUT SIGNALS FROM SAID OSCILLATOR-DETECTOR, C. SWITCHING NETWORK CIRCUIT MEANS COUPLED TO SAID BISTABLE TRIGGER CIRCUIT AND TO SAID OSCILLATOR DETECTOR AND BEING RESPONSIVE SAID FIRST VOLTAGE TO CAUSE SAID OSCILLATOR TO OPERATE AT A FIRST FREQUENCY AND TO SAID SECOND VOLTAGE TO CAUSE SAID OSCILLATOR TO OPERATE AT A SECOND FREQUENCY.

United States Patent Robinson 1 Oct. 14, 1975 BISTABLE FREQUENCY FUZE SYSTEM FOR VT FUZE [75] Inventor: Richard C. Robinson, Whittier,

Calif.

[73] Assignee: The United States of America as represented by the Secretary of the Navy, Washington, DC.

[22] Filed: June 21, 1963 [21] Appl. No.: 289,760

[52] US. Cl. 343/7 PF [51] Int. Cl. F42C 13/04 [58] Field of Search 343/7 PF, 13 SA;

[56] References Cited UNITED STATES PATENTS 3,562,752 2/1971 Roeschke 343/7 PF X Primary ExaminerT. H. Tubbesing Attorney, Agent, or FirmRichard S. Sciascia; Joseph M. St.Amand; T. M. Phillips EXENIPLARY CLAIM 1. In a bistable frequency fuze system for variable time fuzes, the combination comprising:

a. a radio frequency oscillator detector for producing output signals in response to received signals appearing as signals reflected from a target,

b. a bistable trigger circuit being coupled to said oscillator detector for producing first and second output voltages in response to output signals from said oscillator-detector,

c. switching network circuit means coupled to said bistable trigger circuit and to said oscillator detector and being responsive said first voltage to cause said oscillator to operate at a first frequency and to said second voltage to cause said oscillator to operate at a second frequency.

6 Claims, 4 Drawing Figures NETWORK [l2 |4 |6 l8 20 RF BISTABLE OSCILLATOR-b AMPLIFIER TRIGGER 'NTEGRAT'NG DETECTOR CIRCUIT NETWORK SWITCHING US. Patent Oct. 14,1975 Sheet1of2 3,913,102

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[l2 /l4 /l6 Is 20 RF BISTABLE OSCILLATOR-b AMPLIFIER TRIGGER figs $22 V i 's 'gfi DETECTOR CIRCUIT SWITCHING NETWORK FIG. 2

RICHARD C. ROBINSON INVENTOR.

ATTORNEYS U.S. Patent FROM AMPLIFIER OUTPUT Oct. 14, 1975 Sheet 2 of2 3,913,102

TO FREQUENCY SWITCHING 62 NETWORK ssl TURN NETWORK FIRING STEP 'I FROM 0 COUNTER 86 BISTABLE f SWITCHING so CIRCUIT l 84 s9 f 3 as RICHARD c. ROBINSON INVENTOR.

ATTORNEYS BISTABLE FREQUENCY FUZE SYSTEM FOR VT FUZE The present invention relates to a bistable frequency fuze system and more particularly to a bistable frequency fuze system wherein the oscillator is made to provide two widely separated frequencies to prevent the use of jamming techniques on the fuze.

The present invention provides a circuit which significantly reduces VT (variable time) fuze vulnerability to repeater, hunt-lock-on, sweep and/or barrage jamming signals. The accomplishment of this is based on the principle of switching the r-f oscillator frequency between two stable but widely separated operating frequencies. In order to prevent premature firing, more than one cycle of firing level signal is necessary to actuate the firing circuit, and that the fuze switch its operating frequency during each cycle of signal having this amplitude. The reduction of vulnerability to jamming signals is attained by employing a frequency difference between the fuze operating points which exceeds the instantaneous r-f bandwidth characteristics of the jammer equipment. Accordingly an object of the present invention is to provide an improved fuzing system which has reduced vulnerability to jamming signals.

Another object of the present invention is to provide a fuze system which uses a two-level oscillator to provide two widely separated frequencies.

Other objects and many of the attendant advantages of this invention will become readily appreciated as the same becomes better understood by reference to the following detailed description when considered in connection with the accompanying drawings wherein:

FIG. 1 is a block diagram of a typical fuze system embodying the invention.

FIG. 2 is a schematic diagram of the oscillatordetector and switching network of FIG. 1.

FIG. 3 is a schematic diagram of the bistable trigger circuit of FIG. 1.

FIG. 4 is a schematic diagram of the integrating network and firing circuit of FIG. 1.

Referring now to the drawings there is shown in FIG. 1 a block diagram of a typical CW doppler fuze system which comprises a transmit-receive antenna coupled to an r-f oscillator-detector 12 which produces an audio output (doppler) signal. In normal operation the output of oscillator detector 12 is the audio component of the heterodyning of the frequency of the oscillator and the frequency of a target signal due to the doppler frequency shift. In a normal intercept the doppler or beat frequency is initially of a higher frequency than the upper frequency cut-off of amplifier 14. As the range to the target decreases, the rate of change of the range decreases and the beat frequency decreases. If the fuze were allowed to pass by the target, the rate of change of the range would drop to zero at the moment of passing and the beat frequency would be zero at thattime. Therefore, the frequency of the output of detector l2 woulld at some time during intercept be within the acceptance bandwidth of the amplifier 14. At this time the output of the audio amplifier is a quasi- .sinusoidal voltage of both positive and negative polarities which will cause the bistable trigger circuit to function at some time during the first cycle of this signal.

Jamming signals must produce a false target signal in order to be effective. This can be done in several ways such as sweeping the jammer frequency across that of the fuze, locking the jammer on the fuze frequency and introducing a frequency modulation representative of a target signal, or producing frequency translation as in a repeater type jammer. Any of these types of countermeasures create a frequency output of the fuze detector that will appear as a target.

When the jammer produces a false target signal, an audio output signal of positive and negative polarity is produced by detector 12 which passes through amplifier 14 and actuates bistable trigger circuit 16. One output of bistable switching circuit 16 actuates switching network 22 which transfers the RF oscillator detector 12 to its other operating frequency.

The bi-stable." frequency shift (I octave possible) that occurs when an alternating voltage output is present at the amplifier l4 terminals is great enough to create a problem for the jammer to locate the new oscillator frequency. Also, the integrating network 18, which must charge through several successive cycles of frequency switching, discharges during this period while the jammer is hunting for the new fuze frequency and succeeding false-target switching because of the hunting time lag, will not function the fuze. If the target return is present at both oscillator frequencies, switching on a target signal is continuous, and therefore integrating network 18 will continue to charge until the firing circuit 20 input voltage is sufficient to function.

OSCILLATOR-DETECTOR AND SWITCHING NETWORK Referring to FIG. 2 there is shown in detail oscillator detector 12 and switching network 22. The input trigger signal at terminal 26 is received from trigger circuit 16 and coupled through r-f choke 28 to switching network 22 which comprises capacitor 40 and diode 42. Network 22 is connected in shunt with oscillator coil 44 at point 45. Oscillator coil 44 is connected in series between antenna 10 and ground. The detected output signal appears at terminal 46 across load resistor 47. When diode 42 is forward biased, it appears as a small resistance in series with capacitor 40. Effectively, capacitor 40 shunts oscillator coil 44. When diode 42 is reversed biased, it appears as a small (less than 1 uptf), high-Q capacitor in series with capacitor 40. The series capacity combination of capacitor 40 and diode 42 now shunts oscillator coil 44. Therefore, control of the conduction state of diode 42 determines the amount of shunt capacitance across the oscillator tank circuit of oscillator detector 12 which, in turn, controls the oscillator output frequency at antenna 10.

BISTABLE TRIGGER Referring to FIG. 3 there is shown in schematic diagram fonn the bistable trigger circuit 16 of FIG. 1. An output signal from amplifier 14 will appear at input terminal 55. If the signal at terminal 55 is positive, it will be coupled through capacitor 57, diode 58 and resistor 60'to the base of trigistor 48. A negative signal at terminal 55 would be blocked by diode 58 and would appear only at the emitter of trigistor 50. The emitter of trigistor 50 is connected through diode 53 to ground. A negative bias is supplied to the bases of trigistors 48 and 50 through resistors 59 and 61 respectively from terminal through capacitor 54 and diode 62 to junction 65 of the base of trigistor 52, diode 67 and bias resistor 69. The output of trigistor 50 is coupled through capacitor 56 to the emitter of trigistor 52. A negative bias is supplied to diode 67 from terminal 71 of a B- supply, not shown. The base of trigistor 52 is connected to terminal 73 of a B- supply through resistor 69. The emitter of trigistor 52 is connected to terminal 75 of B supply through diode 77 while the collector is connected to terminal 79 of 8+ supply through resistor 81. The output from trigistor 52 is connected to output terminal 83 and through variable resistor 64 to output terminal 85.

The switching of the biased voltage on diode 42 is accomplished by means of the bistable trigger circuit 16 which comprises two monostable trigistors 48 and 50 which trigger a bistable controlled switch 52. Under no signal conditions, trigistors 48 and 50 are normally off. A positive turn-on signal is required at the gate electrode (base) of trigistor 48; a negative turnon signal is required at the cathode (emitter) of trigister 50. The output from each of trigistors 48 and 50 is a negative pulse with the on time for each trigistor being controlled by their respective anode (collector) capacitors 54 and 56. The input series network of diode 58 and resistor 60 to trigistor 48 serve to minimize any transient effects which result during the operation of trigistor 50. The negative pulse output from trigistor 48 is applied through diode 62 to the base of switch 52 and acts as the turn-of signal. The negative pulse from trigistor 50 is applied to the emitter of switch 52 and acts as the turn-on signal. Diode 53 serves as the load for the input signal to trigistor 50.

The negative pulse output from trigistor 48 is applied to the gate of bistable controlled switch 52 and acts as the turn of signal. This is accomplished when the negative pulse from trigistor 48 appears at junction 65 and causes diode 67 to conduct which in turn results in the application of a large negative voltage to the base of trigistor 52.

The negative pulse output from trigistor 50 is applied to the emitter of trigistor 52 and acts as the turn on signal. Diode 77 acts as load for this signal. The negative going portion of the signal instantaneously depresses the emitter voltage of trigistor 52 and lowers its impedance and results in the application of forward voltage to diode 77. During turn-on and tum-off, the output of switch 52 provides forward bias and reverse bias, respectively, for frequency switching diode 42 (FIG. 2). Adjustment of the degree of conduction of diode 42 during turn-on is set by series resistor 64. In addition to providing the trigger signal for frequency switching network 22, the collector of switch 52 supplied a constant amplitude signal to integrating network 18. The high frequency cutoff point which may be different from that determined by the bandpass of amplifier 14 is also controlled by capacitors 54 and 56 and collector resistors 66, 68 and 76 of trigistor 48 and 50. The degree of charge developed across capacitors 54 and 56 during the off-time of trigistors 48 and 50 is frequency sensitive, i.e., the collector voltage and consequently the output pulse amplitude from each trigistor decreases with frequency. Thus, no frequency switching can occur beyond the point at which the trigistors are not capable of initiating the controlled switch.

INTEGRATING NETWORK AND FIRING CIRCUIT The constant amplitude rectangular wave from switch 52 is integrated by integrating network 72 which is a double diode step counter and it includes capacitors 74 and 76 and diodes 78 and 80. The output of integrating network 72 is coupled to firing circuit 20 which is essentially a trigistor 82 connected in series with resistor 84 to a supply voltage source at terminal 86. The circuit may be set to fire after a predetermined number of cycles of switching have occurred from the time that the target signal reaches minimum firing level. Control of the number of cycles required to fire the system is contained in the setting of capacitor 76 and resistor 89. The firing pulse appears at terminal 88.

' SUMMARY The r-f frequency of oscillator 12 is a function of the capacity of capacitor 40. This tank capacity is ,controlled by the conduction state of semi-conductor diode 42. When diode 42 is reversed biased, its capacity is very small; therefore, the total tank capacity (composed of the series combination of capacitor 40 and diode 42) is very nearly the diode capacity (for with the capacity of capacitor 40 being large compared with the capacity of diode 42) and the resultant oscillator frequency is comparatively high. By switching the polarity of biased voltage on diode 42 such that diode 42 is heavily biased in the forward direction, the total tank capacity becomes equal to the capacity of capacitor 40 thus, the oscillator switches to a lower operating frequency.

Obviously many modifications and variations of the present invention are possible in the light of the above teachings. It is therefore to be understood that within the scope of the appended claims the invention may be practiced otherwise than as specifically described.

What is claimed is:

1. In a bistable frequency fuze system for variable time fuzes, the combination comprising:

a. a radio frequency oscillator detector for producing output signals in response to received signals appearing as signals reflected from a target,

b. a bistable trigger circuit being coupled to said 0scillator detector for producing first and second output voltages in response to output signals from said oscillator-detector,

0. switching network circuit means coupled to said bistable trigger circuit and to said oscillator detector and being responsive said first voltage to cause said oscillator to operate at a first frequency and to said second voltage to cause said oscillator to operate at a second frequency.

2. The combination of claim 1 wherein said switching network circuit comprises a capacitor and diode connected in series with the output from said bistable trig ger circuit connected at their common junction.

3. The combination of claim 1 wherein said oscillator detector comprises: i

a. a transmit-receive antenna for transmittingenergy generated by said oscillator and for receiving target reflected energy that was generated by said oscillator,

b. an oscillator coil connected in series between said antenna and a common terminal,

c. an oscillating and detecting vacuum tube having a plate, grid and cathode,

(I. said plate being connected to a B-lvoltage supply through a load resistor,

e. said grid being connected to a mid-tap on said oscillator coil,

f. said cathode being connected to said common terminal and to an A+ voltage supply, and,

g. an output terminal connected to said load resistor.

4. The system of claim 3 wherein said switching network is connected in shunt with said oscillator coil.

5. The system of claim 4 wherein said switching network comprises:

a. a capacitor having a first terminal connected to the mid-tap of said oscillator coil and having a second terminal,

b. a diode having a first terminal connected to the second terminal of said capacitor and having a second terminal connected to said common terminal,

c. circuit means for connecting the output of said bistable trigger circuit to the first terminal of said diode,

d. whereby said first voltage from said trigger circuit will bias said diode in a forward direction to cause said oscillator to oscillate at one frequency and said second voltage from said trigger circuit will bias said diode in the reverse direction and cause said oscillator to oscillate at a second frequency.

6. In a bistable frequency fuze system for variable time fuzes, the combination comprising:

a. a radio frequency oscillator detector having a first and second operating frequencies,

b. first circuit means responsive to output pulses from said oscillator detector for producing first and second bias voltage,

c. second circuit means associated with the tank circuit of said oscillator detector including a diode and being responsive to said first and second bias voltage to cause said oscillator detector to change from one of said operating frequencies to another of said operating frequencies. 

1. In a bistable frequency fuze system for variable time fuzes, the combination comprising: a. a radio frequency oscillator detector for producing output signals in response to received signals appearing as signals reflected from a target, b. a bistable trigger circuit being coupled to said oscillator detector for producing first and second output voltages in response to output signals from said oscillator-detector, c. switching network circuit means coupled to said bistable trigger circuit and to said oscillator detector and being responsive said first voltage to cause said oscillator to operate at a first frequency and to said second voltage to cause said oscillator to operate at a second frequency.
 2. The combination of claim 1 wherein said switching network circuit comprises a capacitor and diode connected in series with the output from said bistable trigger circuit connected at their common junction.
 3. The combination of claim 1 wherein said oscillator detector comprises: a. a transmit-receive antenna for transmitting energy generated by said oscillator and for receiving target reflected energy that was generated by said oscillator, b. an oscillator coil connected in series between said antenna and a common terminal, c. an oscillating and detecting vacuum tube having a plate, grid and cathode, d. said plate being connected to a B+ voltage supply through a load resistor, e. said grid being connected to a mid-tap on said oscillator coil, f. said cathode being connected to said common terminal and to an A+ voltage supply, and, g. an output terminal connected to said load resistor.
 4. The system of claim 3 wherein said switching network is connected in shunt with said oscillator coil.
 5. The system of claim 4 wherein said switching network comprises: a. a capacitor having a first terminal connected to the mid-tap of said oscillator coil and having a second terminal, b. a diode having a first terminal connected to the second terminal of said capacitor and having a second terminal connected to said common terminal, c. circuit means for connecting the output of said bistable trigger circuit to the first terminal of said diode, d. whereby said first voltage from said trigger circuit will bias said diode in a forward direction to cause said oscillator to oscillate at one frequency and said second voltage from said triGger circuit will bias said diode in the reverse direction and cause said oscillator to oscillate at a second frequency.
 6. In a bistable frequency fuze system for variable time fuzes, the combination comprising: a. a radio frequency oscillator detector having a first and second operating frequencies, b. first circuit means responsive to output pulses from said oscillator detector for producing first and second bias voltage, c. second circuit means associated with the tank circuit of said oscillator detector including a diode and being responsive to said first and second bias voltage to cause said oscillator detector to change from one of said operating frequencies to another of said operating frequencies. 